Field of the Invention
The present invention relates to a display device and a driving method thereof, and more particularly, to a display device including a panel with a built-in touch panel and a method of driving the same.
Discussion of the Related Art
Touch panels are a type of input device that is included in display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light emitting display device (OLED), and electrophoretic displays (EPDs), and enables a user to input information by directly touching a screen with a finger, a pen or the like while looking at the screen of the display device.
Particularly, the demand of display devices with integrated in-cell type touch screen, which include a plurality of built-in elements configuring the touch screen for slimming portable terminals such as smart phones and tablet Personal Computers (PCs), is recently increasing.
In an in-cell type display device, as disclosed in U.S. Pat. No. 7,859,521, a plurality of common electrodes for display are segmented into a plurality of touch driving areas and touch sensing areas. An in-cell type display device allows a mutual capacitance to be generated between the touch driving area and the touch sensing area, and thus, measures the change in a mutual capacitance that occurs in touch to determine whether there is a touch.
In other words, in the related art in-cell type display device, a plurality of common electrodes for displaying an image perform the function of a touch electrode when a panel operates in a touch sensing mode, for simultaneously performing a display function and a touch function.
As described above, in a related art in-cell type mutual capacitive display device using the common electrode, the common electrode is used as a driving electrode and a receiving electrode that are necessary for touch sensing, and an image display period and a touch sensing period are temporally divided.
Therefore, in the image display period, a driving electrode and a receiving electrode act as a common electrode. In the touch sensing period, a periodic driving pulse is applied to the driving electrode, and a touch IC determines whether there is a touch by using a sensing signal that is received through the receiving electrode.
FIG. 1 is a waveform diagram showing an image display period and a touch sensing period in a related art in-cell type display device.
In the related art in-cell type display device, as described above and as shown in FIG. 1, a period (hereinafter simply referred to one frame period) corresponding to one frame is divided into an image display period (Display) and a touch sensing period (Touch).
A touch panel applied to a related art in-cell type display device includes a touch electrode to which a common voltage is supplied for an image display period and a driving voltage is supplied for a touch sensing period, and a receiving electrode to which the common voltage is supplied for an image display period and a reference voltage is supplied for a touch sensing period.
For the image display period, the common voltage is supplied to the driving electrode and the receiving electrode. In the touch sensing period, the driving voltage is supplied to the driving electrode, and the reference voltage is supplied to the receiving electrode.
In this case, when one frame period starts, the image display period is first performed, and after the image display period, the touch sensing period is performed. But, the image display period and the touch sensing period may be exchanged.
The above-described in-cell type display devices of the related art have the following problems.
In the related art in-cell type display device, as described above, the touch sensing period for sensing a touch is limited because the image display period is executed after the image display period elapses in one frame period. For example, in a related art in-cell type device which is driven at 60 Hz, sixty images are outputted by using sixty frames for one second, and a sixty-time touch is sensed.
Therefore, in order to sense a touch at a high speed (i.e., at 100 Hz or more), a driving frequency itself of the in-cell type display device should be changed. To this end, a whole configuration of the in-cell type display device should be changed, and thus, it is difficult to actually realize the change.
To provide an additional description, because most of display devices which are recently supplied are configured with a touch panel and all operations of the display devices are driven by a touch, the quick determination of a touch is an important issue.
However, in the related of in-cell type display device, one frame period is divided into an image display period and a touch sensing period, and the touch sensing period is executed after the image display period elapses. Therefore, in one frame period, determining whether there is a touch is performed only one time, and thus, the quick determination of a touch cannot be performed.